In recent years, there is a growing interest in the use of the semiconductor laser as the light source of image display systems. The semiconductor laser has various advantages over the mercury lamp which is commonly used as the light source for more conventional image display systems, such as a better color reproduction, the capability to turn on and off instantaneously, a longer service life, a higher efficiency (or a lower power consumption) and the amenability to compact design.
An example of image display system using a semiconductor laser is disclosed in JP 2007-316393A. Three lasers beams of red, blue and green colors generated by three laser light source units consisting of semiconductor lasers are projected onto a display area of a reflective LCD panel, and the light beams of the different colors imaged and reflected by the reflective LCD panel are projected onto an external screen.
No semiconductor laser that can directly generate a green laser beam at a high power output is available, but it is known to use a laser beam obtained from a semiconductor laser for exciting a laser medium to generate a red laser beam, and convert the red laser beam into a green laser beam by using a nonlinear optical process (wavelength converting device) as disclosed in JP 2008-16833A.
In an image display device such as the one disclosed in JP 2007-316393A, it is possible to display pixels of desired colors either by forming each pixel with a mixture of red, green and blue (RGB) colors (space sharing display system) or by switching between laser beams of red, green and blue colors at high speed for each pixel (time sharing display system).
In the case of the time sharing display system, as it is designed that the laser beams are emitted from a green laser light source unit, a red laser light source unit and a blue laser light source unit in a sequential manner, the laser beams of different colors are not normally emitted simultaneously for each pixel. However, in reality, due to improper laser output control, a plurality of laser beams may be emitted at the same time so that some of the pixels displayed on the screen may become excessively bright, and this is known to cause discomfort to the eyes of the viewer.